SPA-Chemistry - Chemistry of Hand Warmers

LAB ∞: THE CHEMISTRY OF HANDWARMERS. Libby Fones and Maura O’Brien. The purpose of this lab is to duplicate the oxidation reaction in Grabber © Hand Warmers. Pure iron oxidizes when it comes into contact with oxygen (2Fe(s) + 3/2O2(g) à Fe2O3(s)), releasing 822.2 kJ/mol in an exothermic reaction. Most iron available has already oxidized upon contact with air and is already reacted. Acid is a reducing agent, and reacts with iron oxide to form water and iron chloride (FeO(s)+2HCl(aq)àFeCl2(aq)+H2O(l)). Hydrochloric acid converts the top layer of iron (III) oxide to iron (II) chloride and water, exposing the pure iron below. Since iron is a metal, it can take multiple ionic forms depending on the charge of the anion it bonds with. The results of this lab were not promising: even with an acid wash, the iron appeared not to oxidize as no heat was released to the surroundings. This lab was unable to replicate the heat from Grabber © Hand Warmers. Other metals were also investigated with the use of activated carbon. Practical applications of this, if the acid wash were to work, would be the cleaning of rust (a common name for iron (III) oxide). Also, potential effects of pH on iron could be used in determining iron content of water.
Key words: oxidation, reduction, ferrous, acid, specific heat capacity, exothermic, enthalpy.

Summary Graphic:

Summary Graphic.doc

Citations:

Sidhu, P.S, Gilkes, R.J, Cornell, R.M, Posner, A.M, Quirk, J.P. 1981.
Dissolution of Iron Oxides and Oxyhydroxides in Hydrochloric and Perchloric Acids. Clays and Clay Minerals. 29 (4): 269-276.

Neidorff B. April 2007. A Primer on Rust. Available from:
http://www.metalwebnews.com/howto/rust.html (Accessed 2010 Febuary 8)